This invention relates to alumina having a pore structure. This invention further relates to catalysts made from this alumina, from which catalysts may be specifically formulated to provide improved performance characteristics for a great number of hydrocarbon processing operations. This invention also relates to methods of producing this alumina.
The art relating to alumina-containing supports, impregnating such supports with various catalytically active metals, metal compounds and/or promoters, and various uses of such impregnated supports as catalysts, is extensive and relatively well developed. As a few of the many exemplary disclosures relating to these fields may be mentioned the following U.S. patents, all of which are incorporated herein by reference for all purposes as if fully set forth U.S. Pat. Nos. 2,838,444; 2,935,463; 2,973,329; 3,032,514; 3,058,907; 3,124,418; 3,152,865; 3,232,887; 3,287,280; 3,297,588; 3,328,122; 3,493,493; 3,623,837; 3,749,664; 3,778,365; 3,897,365; 3,909,453; 3,983,197; 4,090,874; 4,090,982; 4,154,812; 4,179,408; 4,255,282; 4,328,130; 4,357,263; 4,402,865; 4,444,905; 4,447,556; 4,460,707; 4,530,911; 4,588,706; 4,591,429; 4,595,672; 4,652,545; 4,673,664; 4,677,085; 4,732,886; 4,797,196; 4,861,746; 5,002,919; 5,186,818; 5,232,888; 5,246,569; 5,248,412 and 6,015,485.
While the prior art shows a continuous modification and refinement of such catalysts to improve their catalytic activity, and while in some cases highly desirable activities have actually been achieved, there is a continuing need in the industry for even higher activity catalysts, which are provided by the present invention.
Much of the effort to develop higher activity catalysts has been directed toward developing supports that enhance the catalytic activity of metals that have been deposited thereon. In an overwhelming majority of applications the material chosen for a support is alumina, most often xcex3-alumina, but silica-alumina composites, zeolites and various other inorganic oxides and composites thereof have been and are employed as support materials. In the case of alumina, various researchers have developed methods for preparing supports having various surface areas, pore volumes and pore size distributions that, when appropriate metals are applied, are particularly suited for catalyzing a desired reaction on a particular feedstock, whether that reaction be directed toward hydrodesulphurization, hydrodemetallation, hydrocracking, reforming, isomerization and the like.
Many methods have thus far been proposed for the preparation of alumina. One such method includes aging an aqueous slurry containing seed aluminum hydroxide at a pH of 6-11 for the growth of the seed crystals by coalescence. This method requires a long period of time to obtain hydrogel particles of a large size.
U.S. Pat. Nos. 4,248,852 and 4,422,960 disclose a method for the preparation of alumina suitably used as catalyst carrier, wherein first and second pH controlling agents are alternately and repeatedly mixed with an aqueous slurry containing seed aluminum hydroxide to swing the pH of the slurry between hydrogel dissolution and precipitation regions. At least one of the first and second pH controlling agents includes an aluminum compound capable of forming an alumina hydrogel. Since aluminum hydroxide is continually replenished during the hydrogel growing step, the rate at which the seed aluminum hydroxide grows in size is much higher than that in the method in which the growth of the seed particles is effected by mere coalescence of the seed particles. However, this method has been found to involve a problem in that the resulting alumina carrier does not have entirely satisfactory chemical and physical stability.
U.S. Pat. Nos. 4,562,059 and 4,555,394 disclose a two-stage method for the preparation of alumina suitably used as catalyst carrier, wherein an alumina hydrogel is formed from non-crystalline seed aluminum hydroxide in a first stage and the resultant alumina hydrogel is processed for conversion into alumina in a second stage. The alumina produced by this method is characterized as having the greater part of its pore volume contained within a narrow range of pore diameters; i.e., the alumina manifests a sharp, unimodal pore volume distribution.
In accordance with the present invention, there is provided, in one aspect, an alumina having a novel pore structure. This novel pore structure is characterized by having no more than 5% of the total pore volume in pores greater than 350 xc3x85 (xe2x80x9cmacroporesxe2x80x9d), a high pore volume (greater than 0.8 cc/g measured by mercury intrusion) and a bi-modal pore volume distribution character; i.e., a pore volume distribution in which, when incremental pore volume is plotted as a function of pore diameter, the resulting function exhibits two maxima (also referred to as xe2x80x9cpeaksxe2x80x9d or xe2x80x9cmodesxe2x80x9d herein). These two modes are characterized in that one mode, herein defined as the xe2x80x9cprimary modexe2x80x9d, exhibits a higher maximum than the other mode, which is herein defined as the xe2x80x9csecondary modexe2x80x9d. The primary and secondary modes are separated by at least about 10 xc3x85 and by as much as about 200 xc3x85. The primary pore mode occurs at a pore diameter greater than the median pore diameter (xe2x80x9cMPDxe2x80x9d), calculated either by volume or by surface area. Median pore diameter calculated by volume (xe2x80x9cMPDVxe2x80x9d) herein means the pore diameter above which half of the total pore volume exists; median pore volume calculated by surface area (xe2x80x9cMPDSAxe2x80x9d) means that pore diameter above which half of the total pore surface area exists. In the alumina of the present invention, the MPDV is larger than the MPDSA.
Also provided in this invention is a method of making such alumina. This method involves process steps that are similar to those taught in an earlier patent (U.S. Pat. No. 4,555,394). In the present invention, however, the seeds produced in the first stage need not be non-crystalline, no limits on the addition rates of aluminum components to the second stage are imposed and the alumina produced exhibits novel pore size distribution patterns. Indeed, by appropriate adjustment of the processing conditions used in the production of the alumina of the present invention, the final pore size distribution of the alumina support can be tailored to a specific catalytic application.
In another aspect, the present invention provides high activity catalysts comprising supports based upon the alumina of the present invention and impregnated with one or more metals.
These and other features and advantages of the present invention will be more readily understood by those of ordinary skill in the art from a reading of the following detailed description.